I am using fix Thermal/conductivity to measure thermal conductivity of a box of water using Muller-Plathe algorithm. Actually I am swapping one atom every 10 timesteps. when I draw temperature of the first and the middle layers, I see an interesting thing happening... Both layers are increasing in temperature with time. As you know, I am working with an NVE ensemble and I expect it to conserve energy, but total kinetic energy is increasing in time. Anyone knows why this happens?